The fibroblast growth factor (FGF) family is characterized by 22 genetically distinct, homologous ligands, which are grouped into seven subfamilies. FGF-21 is most closely related to, and forms a subfamily with, FGF-19 and FGF-23. This FGF subfamily regulates diverse physiological processes uncommon to classical FGFs, namely energy and bile acid homeostasis, glucose and lipid metabolism, and phosphate as well as vitamin D homeostasis. Moreover, unlike other FGFs, this subfamily acts in an endocrine fashion. (Moore, D. D. (2007) Science 316, 1436-8)(Beenken et al. (2009) Nature Reviews Drug Discovery 8, 235).
FGF21 is a 209 amino acid polypeptide containing a 28 amino acid leader sequence (SEQ ID NO:5). Human FGF21 has about 79% amino acid identity to mouse FGF21 and about 80% amino acid identity to rat FGF21. Fibroblast growth factor 21 (FGF21) has been described as a treatment for ischemic vascular disease, wound healing, and diseases associated with loss of pulmonary, bronchia or alveolar cell function. (Nishimura et al. (2000) Biochimica et Biophysica Acta, 1492:203-206; patent publication WO01/36640; and patent publication WO01/18172) Although FGF-21 activates FGF receptors and downstream signaling molecules, including FRS2a and ERK, direct interaction of FGFRs and FGF-21 has not been detected. Studies have identified β-klotho, which is highly expressed in liver, adipocytes and pancreas, as a determinant of the cellular response to FGF-21 and a cofactor which mediates FGF-21 signaling through FGFRs (Kurosu, H. et al. (2007) J Biol Chem 282, 26687-95). FGF21 is a potent agonist of the FGFR1(IIIc), FGFR2(IIIc) and FGFR3(IIIc) 3-klotho signaling complexes.
FGF-21 has been shown to induce insulin-independent glucose uptake. FGF-21 has also been shown to ameliorate hyperglycemia in a range of diabetic rodent models. In addition, transgenic mice over-expressing FGF-21 were found to be resistant to diet-induced metabolic abnormalities, and demonstrated decreased body weight and fat mass, and enhancements in insulin sensitivity (Badman, M. K. et al. (2007) Cell Metab 5, 426-37). Administration of FGF-21 to diabetic non-human primates caused a decline in fasting plasma glucose, triglycerides, insulin and glucagon levels, and led to significant improvements in lipoprotein profiles including a nearly 80% increase in HDL cholesterol (Kharitonenkov, A. et al. (2007) Endocrinology 148, 774-81). Recent studies investigating the molecular mechanisms of FGF21 action have identified FGF21 as an important endocrine hormone that helps to control adaptation to the fasting state. (Badman et al. (2009) Endocrinology 150, 4931)(Inagaki et al. (2007) Cell Metabolism 5, 415) This provides a previously missing link downstream of PPARα, by which the liver communicates with the rest of the body in regulating the biology of energy homeostasis. (Galman et al. (2008) Cell Metabolism 8, 169)(Lundasen et al. (2007) Biochemical and Biophysical Research Communications 360, 437).
FGF21 regulates adipocyte homeostasis through activation of an AMPK/SIRT1/PGC1α pathway to inhibit PPARγ expression and increase mitochondrial function. (Chau et al. (2010) PNAS 107, 12553) FGF21 also increases glucose uptake by skeletal muscle as measured in cultured human myotubes and isolated mouse tissue. FGF21 treatment of rodent islet cells leads to improved function and survival through activation of ERK½ and Akt pathways. (Wente et al. (2006) Diabetes 55, 2470) FGF21 treatment also results in altered gene expression for lipogenesis and fatty acid oxidation enzymes in rodent livers, likely through HNF4α and Foxa2 signaling.
A difficulty associated with using FGF-21 directly as a biotherapeutic is that its half-life is very short. (Kharitonenkov, A. et al. (2005) Journal of Clinical Investigation 115:1627-1635) In mice, the half-life of human FGF21 is 0.5 to 1 hours, and in cynomolgus monkeys, the half-life is 2 to 3 hours. FGF21 may be utilized as a multi-use, sterile pharmaceutical formulation. However, it has been determined that preservatives, i.e., m-cresol, have an adverse affect on its stability under these conditions.
In developing an FGF21 protein for use as a therapeutic in the treatment of type 1 and type 2 diabetes mellitus and other metabolic conditions, an increase in half-life and stability would be desirable. FGF21 proteins having enhanced half-life and stability would allow for less frequent dosing of patients being administered the protein. Clearly, there is a need to develop a stable aqueous protein formulation for the therapeutic protein FGF21.
Furthermore, significant challenge in the development of FGF21 as a protein pharmaceuticals, is to cope with its physical and chemical instabilities. The compositional variety and characteristics of proteins define specific behaviors such as folding, conformational stability, and unfolding/denaturation. Such characteristics should be addressed when aiming to stabilize proteins in the course of developing pharmaceutical formulation conditions utilizing aqueous protein solutions (Wang, W., Int. J. of Pharmaceutics, 18, (1999)). A desired effect of stabilizing therapeutic proteins of interest, e.g., the proteins of the present invention, is increasing resistance to proteolysis and enzymatic degradation, thereby improving protein stability and reducing protein aggregation.